Here is a PDF file that on a couple of pages shows how to use the astro compass to determine true north, and examples are given. Two methods are shown.

The illustratingShadows.xls spreadsheet (in the zip file to the left) supports the second method. The astro compass can also be used to tell the time accurately, being a variation of the armillary dial.

CLICK HERE for the astro compass notes. [NOTE: the examples are set in New Mexico and AZ, USA as regards longitude]I have had these things on and off since I was a late teen, as well as bubble and fixed horizon sextants, and almost anything that came out of world war 2 ships and planes. They can be found on Ebay fairly easily for less than $100, and these notes tell you how to use it, and tell how to make the mount out of a bit of PVC pipe. Without that mount, the levelling system will not work. I have Excel sheets for the PC as well as Documents To Go to facilitate astro compass usage.

Anyhow, after you have seen some of these articles on this web site, you may want to purchase the book itself, Illustrating Time's Shadow (printed, or online download) buy here!

This table comes from a spreadsheet which allows you to adjust the astro compass hour angle for longitude and EOT. The master spreadsheet (Excel)has this and other valuable sheets. There is also a version specifically for the Palm Pilot.

Only two adjustments (which the main spreadsheet does for you), one is to correct for longitude offset from the standard time meridian, the other is the EOT.